Inouye spent most of his Senate career attending to Hawaii. At the height of his power, Inouye routinely secured tens of millions of dollars annually for the state's roads, schools, national lands and military bases.
Although tremendously popular in his home state, Inouye actively avoided the national spotlight until he was thrust into it. He was the keynote speaker at the 1968 Democratic National Convention, and later reluctantly joined the Senate's select committee on the Watergate scandal. The panel's investigation led to the resignation of President Richard Nixon.
Inouye also served as chairman of the committee that investigated the Iran-Contra arms and money affair, which rocked Ronald Reagan's presidency.
A quiet but powerful lawmaker, Inouye ran for Senate majority leader several times without success. He gained power as a member of the Senate Appropriations Committee and chairman of the defense appropriations subcommittee before Republicans took control of the Senate in 1994.
When the Democrats regained control in the 2006 elections, Inouye became chairman of the Senate Commerce Committee. He left that post two years later to become chairman of the powerful Senate Appropriations Committee.
Inouye also chaired the Senate Indian Affairs Committee for many years. He was made an honorary member of the Navajo nation and given the name "The Leader Who Has Returned With a Plan."
He is the last remaining member of the Senate to have voted for the Civil Rights Act of 1964.
Inouye was serving as Hawaii's first congressman in 1962, when he ran for the Senate and won 70 percent of the vote.
In 1968, President Lyndon Johnson urged Vice President Hubert Humphrey, who had won the Democratic nomination for president, to select Inouye as his running mate. Johnson told Humphrey that Inouye's World War II injuries would silence Humphrey's critics on the Vietnam War.
"He answers Vietnam with that empty sleeve. He answers your problems with (Republican presidential candidate Richard) Nixon with that empty sleeve," Johnson said.
But Inouye was not interested.
"He was content in his position as a U.S. senator representing Hawaii," Jennifer Sabas, Inouye's Hawaii chief of staff, said in 2008.
In one of the most memorable exchanges of the Watergate proceedings, an attorney for two of Nixon's closest advisers referred to Inouye as a "little Jap."
The attorney, John J. Wilson, later apologized. Inouye accepted the apology, noting that the slur came after he had muttered "what a liar" into a microphone that he thought had been turned off following Ehrlichman's testimony.
Inouye was born Sept. 7, 1924, to immigrant parents in Honolulu. After the Pearl Harbor bombings changed the course of his life, he volunteered for the Army at 18 and was assigned to the famed Japanese-American 442nd Regimental Combat Team. The team earned the nickname "Go For Broke." Inouye rose to the rank of captain and earned the Distinguished Service Cross and Bronze Star.
His military unit became the most highly decorated ever for its size and length of service.
Unlike the families of many of his comrades in arms, Inouye's wasn't subjected to the trauma and indignity of being sent by the U.S. government during the war to internment camps for Japanese Americans.
"It was the ultimate of patriotism," Inouye said at a 442nd reunion. "These men, who came from behind barbed wire internment camps where the Japanese-Americans were held, to volunteer to fight and give their lives. ... We knew we were expendable."
Inouye spent the next 20 months after losing his right arm in military hospitals. During his convalescence, Inouye met Bob Dole, the future majority leader of the Senate and 1996 Republican presidential candidate, who also was recovering from severe war injuries.
"With Sen. Inouye, what you saw is what you got and what you got was just a wonderful human being that served his country after the ill-treatment of the Japanese, lost an arm in the process," Dole said Monday. "He was the best bridge player on our floor. He did it all with one arm."
Despite his military service and honors, Inouye returned to an often-hostile America. On his way home from the war, he often recounted, he entered a San Francisco barbershop only to be told, "We don't cut Jap hair."
He returned to Hawaii and received a bachelor's degree in government and economics from the University of Hawaii in 1950. He graduated from George Washington University's law school in 1952.
Inouye proposed to Margaret Shinobu Awamura on their second date, and they married in 1949. Their only child, Daniel Jr., was born in 1964. When his wife died in 2006, Inouye said, "It was a most special blessing to have had Maggie in my life for 58 years."
He remarried in 2008, to Irene Hirano, a Los Angeles community leader.
Oskar Garcia can be reached on Twitter at http://twitter.com/oskargarcia .
Associated Press writers Andrew Taylor in Washington and Audrey McAvoy and Becky Bohrer in Honolulu contributed to this report.